Apparatus for controlling relative motion between gage jaws on a contacting gage

ABSTRACT

An apparatus for controlling the relative motion and final position between gage jaws on a contacting type of gage. A driving mechanism is coupled to one of the gage jaws to provide relative motion between said jaws. A command circuit supplies command signals to the driving mechanism. Each time the driving mechanism is commanded to move, a feed back circuit measures the actual motion of the gage jaw and produces a control signal in response to a predetermined magnitude of said motion. The control signal is used to gate a subsequent command signal to the driving mechanism. Consequently, the gage jaw can be brought in contact with a workpiece and held in position thereon without the danger of damage to the workpiece.

United States Patent Fischer 3,700,993 14s] Oct. 24, 1972 PrimaryExaminer-Benjamin Dobeck Attorney-Howard T. Keiser and C. Richard Eby[72] Inventor: Thomas R. Fischer, Cincinnati, Ohio [73] Assignee:Cincinnati Milacron, Inc., Cincin- ABSTRACT nati, 01110 An apparatus forcontrolling the relative motion and 2 Filed; May 27, 1971 final positionbetween gage jaws on a contacting type of gage. A driving mechanism iscoupled to one of the [21] APPI- N04 147,432 gage jawsto providerelative motion between said jaws. A command circuit supplies commandsignals to 52] US. Cl ..318/603, 318/600 the driving mechanism. Eachtime the driving [51] Int. (:1. ..G05b 19/28 mechanism is commanded to ma feed back [58] Field of Search 318/603 608 600 601 646 cuit measuresthe actual motion of the gage jaw and produces a control signal inresponse to a predetermined magnitude of said motion. The control signalis [56] References Cited used to gate a subsequent command signal to thedriv- UNITED STATES PATENTS ing mechanism. Consequently, the gage jawcan be brought in contact with a workpiece and held in posigfi gi tionthereon without the danger of damage to the work iece 3,519,904 7/1970Rogers ..3l8/608 p 3,564,379 2/ 1971 Bakel et al ..318/608 4 Claims, 4Drawing Figures SM SM DRIVE CONTROL INPUT SM 38 COMMAND CIRCUIT 47 2a 44I v OSCILLATOR CIRCUIT s25 5h ,flo n I coum G fli 40 DIRECTION I COUNTERDECODER 58 a I FEEDBACK MEAS cm 52" APPARATUS FOR CONTROLLING RELATIVEMOTION BETWEEN GAGE JAWS ON A CONTACTING GAGE BACKGROUND OF THEINVENTION The invention relates generally to the area of gagecontrollers. Specifically, the invention provides a control for acontacting type of gage which automatically brings the gage jaws incontact with the workpiece in a gages. Non-contacting gages are morereadily adapted to an automatic control because the relative position ofthe gage jaws with respect .to the workpiece is less critical than in acontacting gage. However, a non-contacting pneumatic gage is moresusceptible to contamination and inaccuracies than a contacting gage.This is a result of air and coolant films that surround the workpieceand influence the measurement.

Generally, because of its greater reliability and accuracy, anelectronic gage is more desirable than a pneumatic gage. However,contact pressure is a very critical parameter that is difficult to placeunder automatic control. The ultimate contact pressure is always acompromise. For example, a minimal contact pressure is desirable becausethe accuracy is greater. Further, errors due to structural deflectionsof the gage are less; and the marking of the part is held to a minimum.But, as a practical matter, the contact pressure must be increased toguarantee a high degree of repeatability of the contact force. Inaddition a higher contact pressure is required for the gage anvils topenetrate any fluid further complicated when placing a contacting gageunder automatic control. Generally, the anvils on each gage jaw have arelatively small area of contact with the workpiece. Therefore, only aminimal force is required for the anvils to pierce the fluid filmssurrounding the workpiece. However, in order to guarantee that the gageis always measuring a true diameter, the anvils in an automatic gagehave a larger area of contact on the workpiece. Hence, a greater contactpressure is necessary. In view of the above, one can readily appreciatewhy the control of contacting gages has been slow to develop. Applicantproposes an apparatus for automatically controlling a contacting gage.The apparatus accurately brings the gage jaws in contact with theworkpiece and maintains an effective contact pressure without damagingthe surface of the workpiece.

SUMMARY OF THE INVENTION The present invention discloses an apparatusfor use with a gaging device wherein a relative motion between two gagejaws is generated by a driving mechanism in response to a commandsignal. A feed back element senses the actual relative motion betweenthe gage jaws and produces feed back signals. A feed back controlcircuit is responsive to the feed back signals to produce a controlsignal in response to a predetermined magnitude of relative motion. Thecontrol signal is operative to control the application of successivecommand signals to the driving mechanism.

- BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a general block diagram ofthe invention.

FIG. 2 is a detailed block diagram of the preferred embodimentinvention.

FIG. 3a is a detailed schematic diagram of the direction decoder andreversible counter used in applicants invention. v a

FIG. 3b is detailed schematic diagram of an alternative embodiment ofthe count decoder.

FIG. 4 is a timing diagram illustrating the operation of the directiondecoder and counter.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a general blockdiagram of the invention. FIG. 1 illustrates the general gageconfiguration, and it should be understood that the gage constructiondisclosed does not place a limitation on the application of thedisclosed invention. It should further be noted that the positioning ofthe gage structure itself with respect to the center line of theworkpiece is shown in the prior art and deemed to be within theknowledge of those who are skilled in the art. Applicants disclosedinvention pertains to the control of the gage jaws themselves.

The gage contains a lower jaw 10 and upper jaw 12. The upper jaw 12 ismovably mounted in the structure 14 and is under the influence of amechanical bias. The structure of the gage head will be described inmore detail later in the specification. Anvils 11 and 13 are located onthe lower and upper jaws l0 and 12 respectively and are operative tocontact the workpiece 15 when the gage jaws are brought together. Adriving mechanism 16 is mechanically coupled to the upper jaw 12 toprovide a linear motion of the upper jaw 12 with respect to the lowerjaw 10. The driving mechanism is responsive to a command signal producedby a command control 18. There are a number of driving mechanisms thatmay be used. For example, the driving mechanism may be a piston andcylinder, an electrohydraulic motor or an electric motor. In addition,the command circuit 18 may have its signals generated by a manualselection of switches or may be derived from a programmed input. Thegeneration of command signals which are necessary for any particulardriving mechanism is well-known to those who are skilled in the art. Afeed back element 20 is coupled to the gage jaws and generates feed backsignalsdefining the direction and magnitude of motion of the upper jaw12 with respect to the lower jaw 10. A feed back control circuit 22 isresponsive to the feed back signals to produce a control signal inresponse to a relative motion between the jaws of a predeterminedmagnitude and in a predetermined direction. The control signal is oneinput of a gating network 24 having another input responsive to thecommand signal and an output connected to the driving mechanism. Thegating network 24 is operative to apply a command signal to the drivingmechanism in response to the occurrence of a control signal, and thegating network 24 terminates the command signal output to the drivingmechanism in response to an absence of the control signal. Hence, the

driving mechanism is only supplied with a command signal if the upperjaw has moved a predetermined distance in response to a prior commandsignal. Conture 14 under a mechanical bias the contact pressure can beincreased by continuing the application of the command signal for apredetermined period of time.

FIG. 2 is a detailed block diagram of the preferred embodiment of theinvention. A lower gage jaw 26 containing an anvil 27 is fixed to a gagestructure 28. An upper gage jaw 30 containing an anvil 31 is slidablymounted within the structure 28. A ball screw 32 is rotatably mounted atone end to a nut 34 rigidly fixed to the upper jaw 30. The other end ofthe ball screw 32 is connected through a coupling 36 to a stepping motor38. The coupling 36 permits a substantial axial motion but does notallow any rotational motion between the stepping motor and ball screw.Further, the coupling 36 is under a mechanical bias which provides aforce on the upper jaw toward the workpiece. Consequently, the ballscrew 32, nut 34 and upper jaw 30 float with respect to the steppingmotor 38 and gage structure 28.

Gages of this structure are commercially available, and furtherdisclosure of the gage itself should be unnecessary. The stepping motor38 is energized by a stepping motor drive circuit 42 which generally issupplied with any commercial stepping motor. The stepping motor drivecircuit 42 is energized by a stepping motor control circuit 44. Thestepping motor control circuit is responsive to an input command circuit46 which produces signals defining when and in what direction thestepping motor is to move. In addition, the control circuit 44 isresponsive to command pulses from an oscillator. circuit 48. Eachcommand pulse, defines an increment of motion of the stepping motor 38and hence the upper gage jaw 30. The frequency of occurrence of thecommand pulses determines the velocity of the motor 38. The inputcommand circuit 46 also produces signals on line 47 to the oscillatorcircuit 48 which are operative to change the frequency of the oscillatoroutput and hence the velocity of the motor 38. From the diagram of FIG.2, it can be readily appreciated that the stepping motor 38, steppingmotor drive 42 and stepping motor control circuits 44 operate as adriving mechanism. Further, the oscillator circuit 48 and input commandcircuits 46 combine to function as a command control. Since the use ofstepping motors and their control is generally well-known; and further,since a particular embodiment of a driving mechanism is not important tothe disclosed invention, the'circuits discussed above need not be shownin more detail.

Affixed to the upper jaw 30 is a portion of a feed back element 40awhich has a mating portion 40b affixed to the gage structure 28. Thefeed back element 40 is operative to produce two feed backs signals.Each signal being a square wave, and said signals being 90 out of phasewith each other. The feed back signals are input to a direction decoder50 which is operative to detect which direction the upper gage jaw 30 ismoving. An output signal from the direction decoder 50 is input to afeed back measuring circuit 52 comprised of a reversible counter 54 anda count decoder 56. The counter 54 measures the magnitude of motion ofthe upper jaw 30 in both directions and the count decoder 56 produces acontrol signal in response to a predetermined magnitude of motion in aparticular direction. The control signal is input to a gating network 58having another input connected to the oscillator circuit 48 and anoutput connected to the stepping motor control circuit 44. The controlsignal is operative to control the application of command pulses to thestepping motor control circuit 44 as a function of the actual distancemoved by the upper gage jaw in response to previous command pulses. Theoperation of this circuit will be made clearer by reference to FIGS. 3and 4.

FIG. 3a is a detailed schematic diagram of the direction decoder and thereversible counter. FIG. 4 is a timing diagramof various signals withinthe feed back control circuit. Curve 1 of FIG. 4 represents one periodof a command pulse from the oscillator circuit 48, and said periodrepresents a predetermined increment of motion of the upper gage jaw 30,e.g., 0.002 inches. Curves 2 and 3 represent feed back signals from thefeed back element 40. Curve 2 will arbitrarily be called the X-feed backsignal, and curve 3 the Y-feed back signal. Further it should be notedthat the feed back signals are 90 out of phase. In addition, there are anumber of, e.g., l0, feed back signal periods in each period of thecommand pulse. Therefore, with the example values used above each periodof the X and Y feed back signals represents 0.0002 inches of motion ofthe upper gage jaw. In FIG. 3a, the direction decoder is sensitive tothe 90 phase shift between the feed back signals for determining thedirection of motion. NAND gates 60, 62 and 68 and flip flops 64 and 66detect the relationship between the X-feed back signal'and the Y- feedback signal. If the upper jaw 30 is moving toward the lower' jaw 26, theabove logic elements will generate an output on NAND 68 which may berepresented by curve 4 of FIG. 4. If the upper jaw 30 is moving .awayfrom the lower jaw 26, the above elements will not produce any signal onthe output of NAND 68. However, this motion will cause NAND gates 70, 72and 78 and flip flops 74 and 76, which de- 'tect the relationship of theX-feed back signal to the not Y-feed back signal, to produce an outputfrom the gate '78. Therefore, motion of the upper gage jaw away from thelower gage jaw produces an output signal from the NAND gate 78 which isrepresented by the curve of 5 of FIG. 4.

The output of gages 68 and 78 are tied together and used as a clockingsignal in the reversible counter comprised of flip flops 80 through 88.The particular embodiment of the counter is an arbirtrary designdecision. For example, there are 10 feed back signals periods for eachperiod of the command pulse. Therefore, on each command pulse thequantity 10 could be set into the counter and the feed back signals usedto clock the counter to zero. Hence, the detected zero state could thenbe used to gate the next command pulse. However, applicant has chosen touse the command pulse itself to set a number in to the counter.Consequently, the counter will be inoperative for one half of thecommand pulse; and therefore, one will only be able to count five feedback'signal periods. Further, since the system cannot be depended uponto move exactly 0.002 inches for each command pulse, it is unreasonableto expect exactly five feed back signal periods during one half a periodof the command pulse.

l lowever, one would always expect to see four feed back signal periods.Therefore, the command pulse signal is used to set flip flop 84 in thecounter. Setting this flip flop represents the loading of a number 4. Asthe upper gage jaw proceeds toward the workpiece, one-half of eachcommand pulse period is used to set the number 4 into the counter; andduring the other half cycle clock pulses produced by the NAND gate 68 inconjunction with NAND gates 90 through 96 cause the counter to countdown to zero. The zero state is detected by a count decoder comprised ofNAND gate 98 which produces a control signal in response to the zerostate. The control signal is used to gate another command pulse to thedriving mechanism as earlier described,and the counting process repeats.

Eventually a point is reached where the upper gage jaw contacts theworkpiece. As a result, the terminationof motionis indicated by thetermination of feed back signals. Hence, the counter does not reach azero state, and no further command pulses are gated to the drivingmechanism because no more control signals are produced. The gage jawsare resting on the surfaceof the workpiece, and the measuring process bythe gage begins. As a practical matter, with the feed back elementsensitive to a motion of 0.0002 inches or more, the feed back signals donot terminate. The surface of the workpiece may be rough, and theworkpiece may be out of round. Consequently, the gage jaws continuouslymove away from and toward the center line of the workpiece as a functionof the eccentricities in the surface of the workpiece. The feed backsignals are continuously-indicating an oscillatory motion. The magnitudeof this motion is measured by the counter circuit. If the gage jaw movesout, the clock pulses produced by NAND gate 78 along with NAND gates 100through 106 cause the counter to count up; and as the gage jaw movestoward the workpiece, the counter counts down. Therefore, with respectto any particular command pulse, the counter maintains a signalrepresenting the absolute value of motion of the gage jaw; and asubsequent command pulse will not be applied to the driving mechanismuntil a particular magnitude of motion, e.g., 4 counts or 0.0008 inches,is detected toward the workpiece.

As described earlier, the gaging pressure must be heavy enough to holdthe gage jaws firmly in place, but light enough to produce an accurateand reliable measurement of the workpiece. With the upper gage jaw gagejaw comes in contact with the workpiece. Therefore, as shown in FIG. 3b,it may be desirable to use a time delay 108 to control the gating ofcommand pulses. Each time the NAND gate 98 produces an output signalindicating a predetermined position of the gage jaw, the time delay isinitiated and produces a control signal gating successive command pulsesfor the time well-known to those who are skilled in the art, and furtherdiscussion should not be necessary.

In summary, in a gaging apparatus where the gage jaws are'controlled bya positive mechanical driving mechanism, an apparatus is provided forpositively 'contact'the workpiece, no further motion is detected;

and the operation of the driving mechanism is terminated. Further, it isdisclosed how to use theabove system to adjust the gaging pressure onthe workpiece.

While invention has been illustrated in some detail according to thepreferred embodiments shown in the accompanying drawings, and while thepreferred illustrated embodiments have been described in some detail,there is no intention to thus limit the invention to such detail. On thecontrary, it is intended to cover all modifications, alterations andequivalents falling within the spirit and scope of the appended claims".

What is claimed is:

1. An apparatus for controlling relative. motion between gage jaws in agaging device, one of said gage jaws being coupled to a drivingmechanism for moving it relative to the other gage jaw in response tocom mand pulses representing predetermined commanded increments ofmotion, the apparatus comprising:

a. a feedback element connected to the gage jaws and being responsive toa first command pulse for producing two periodic pulse trains shifted inphase with respect to each other, said pulse trains having a periodrepresenting a predetermined magnitude of motion being a predeterminedfractionof the commanded increment of motion;

b. a direction decoder connected to the feedback element for detectingthe direction of the relative motion between the gage jaws;

, c. a reversible counter responsive to the first command pulse andconnected to the feedback element and the direction decoder formeasuring the magnitude of the relative motion between the gage jaws; r

d. a count decoder connected to the counter for producing a controlsignal in response to a predetermined magnitude of motion measured bythe counter in a predetermined direction; and

. a gating network responsive to the control signal and the commandpulses and having an output connected to the driving mechanism forproducing a second command pulse to the driving mechanism in response tothe control signal and inhibiting the production of the second commandpulse to the driving mechanism in response to an absence of the controlsignals.

2. The apparatus of claim 1 wherein a time delay is connected betweenthe count decoder and the gating network for maintaining the controlsignal for a predetermined period of time. p

3. An apparatus for use with a gaging device for controlling motion of afirst gage jaw relative to a second gage jaw, said motion beinggenerated by a drivingmechanism coupled to the gaging device andoperating in response to a first command signal representing a,

predetermined increment of motion, the apparatus comprising:

a. means responsive to the relative motion between the gage jaws forproducing two feedback signals, each feedback signal representing apredetermined fraction of the increment of motion;

b. means responsive to the feedback signals for producing a controlsignal in response to a predetermined number of one of said feedbacksignals occurring during a relative motion in a 10 predetermineddirection; and

I c. means responsive to the control signal and having an outputconnected to the driving mechanism for controlling the application of asecond command signal to the driving mechanism.

4. An apparatus for controlling relative motion between first and secondgage jaws of a gaging device, said relative motion being generated by adriving mechanism connected to the gaging device and operating inresponse to command pulses, each command pulse representing apredetermined increment of motion, the apparatus comprising:

a. means responsive to a relative motion between the responsive to oneof the feedback signals and thefirst command pulse for producing acontrol signal in response to a predetermined number of the one of thefeedback signals occurring during a relative motion in a predetermineddirection; and

d. means responsive to the control signal and a second command pulse andhaving an output connected to the driving mechanism for supplying saidsecond command pulse to the driving mechanism in response to the controlsignal.

1. An apparatus for controlling relative motion between gage jaws in agaging device, one of said gage jaws being coupled to a drivingmechanism for moving it relative to the other gage jaw in response tocommand pulses representing predetermined commanded increments ofmotion, the apparatus comprising: a. a feedback element connected to thegage jaws and being responsive to a first command pulse for producingtwo periodic pulse trains shifted in phase 90* with respect to eachother, said pulse trains having a period representing a predeterminedmagnitude of motion being a predetermined fraction of the commandedincrement of motion; b. a direction decoder connected to the feedbackelemEnt for detecting the direction of the relative motion between thegage jaws; c. a reversible counter responsive to the first command pulseand connected to the feedback element and the direction decoder formeasuring the magnitude of the relative motion between the gage jaws; d.a count decoder connected to the counter for producing a control signalin response to a predetermined magnitude of motion measured by thecounter in a predetermined direction; and e. a gating network responsiveto the control signal and the command pulses and having an outputconnected to the driving mechanism for producing a second command pulseto the driving mechanism in response to the control signal andinhibiting the production of the second command pulse to the drivingmechanism in response to an absence of the control signals.
 2. Theapparatus of claim 1 wherein a time delay is connected between the countdecoder and the gating network for maintaining the control signal for apredetermined period of time.
 3. An apparatus for use with a gagingdevice for controlling motion of a first gage jaw relative to a secondgage jaw, said motion being generated by a driving mechanism coupled tothe gaging device and operating in response to a first command signalrepresenting a predetermined increment of motion, the apparatuscomprising: a. means responsive to the relative motion between the gagejaws for producing two feedback signals, each feedback signalrepresenting a predetermined fraction of the increment of motion; b.means responsive to the feedback signals for producing a control signalin response to a predetermined number of one of said feedback signalsoccurring during a relative motion in a predetermined direction; and c.means responsive to the control signal and having an output connected tothe driving mechanism for controlling the application of a secondcommand signal to the driving mechanism.
 4. An apparatus for controllingrelative motion between first and second gage jaws of a gaging device,said relative motion being generated by a driving mechanism connected tothe gaging device and operating in response to command pulses, eachcommand pulse representing a predetermined increment of motion, theapparatus comprising: a. means responsive to a relative motion betweenthe gage jaws produced by a first command pulse for producing periodicfeedback signals, each feedback signal having a period representing afraction of the predetermined increment of motion, and one of saidfeedback signals being displaced in time by one quarter of a period withrespect to the other feedback signal; b. means responsive to thefeedback signals for detecting the direction of motion of the firstgaged jaw with respect to the second gage jaw; c. means connected to thedetecting means and responsive to one of the feedback signals and thefirst command pulse for producing a control signal in response to apredetermined number of the one of the feedback signals occurring duringa relative motion in a predetermined direction; and d. means responsiveto the control signal and a second command pulse and having an outputconnected to the driving mechanism for supplying said second commandpulse to the driving mechanism in response to the control signal.